Tuesday, July 26, 2005

So what’s the deal with Circular logging, and how does this apply to the SBS 2003 world?

First of all, there are quite a number of resources available on the Microsoft Knowledge base that relate to this topic. The problem is that if you read enough of them, you’ll probably end up just as confused as when you started. So let me try and make some sense of this for you.

You might notice that on a fresh install of SBS 2003, that circular logging is actually enabled (and stays that way until you run the backup-wizard). Contrast this to Exchange 2000/2003 Standard or Enterprise, where circular logging is disabled. Why the discrepancy? Probably because enough people called up product support services complaining that they were out of drive space, and that upon further investigation, support determined that they were out of drive space because they were hanging onto all of those transaction logs.

So what is circular logging? Well, it’s basically a log-recycler. After Exchange fills up the first 4 logs, circular logging assumes that it’s okay to start re-writing the first one. So you can see the problem – circular logging sacrifices redundancy in order to preserve drive space. This also breaks differential and incremental backup procedures. So you’ll have to do full backups.

What should you do?

At the very least, use the SBS-supplied wizard-interface to NTbackup. And make sure you are actually getting good backups. Do test restores as part of your Exchange maintenance policy.

What do I recommend?

I recommend Veritas Backup Exec. If you’re in the SBS world, Veritas makes a version specific to SBS, which includes an Exchange agent at a reasonable price ($437 for as of 7/05). You can search for manufacturer part number “A130478-0LB000”. But keep in mind that this will only let you backup your SBS server. You can’t purchase additional agents to backup any member servers that you might have in your environment. So if you have any member servers in your SBS environment that you need to backup (and you should be backing these up), you’ll probably need to get the full version of Backup Exec (which is quite expensive).